1. Field of the Invention
The present invention relates generally to belt aligning and tracking rollers for conveyor belt systems and more particularly to an improved tracking roller having variable pitch helical guides for providing faster tracking ability.
2. Description of Prior Art
Maintaining the alignment of conveyor webs or belt shaped materials over rollers or pulleys has been a universal problem. Tracking rollers having helical grooves or ribbing which significantly improve tracking have been disclosed in my earlier U.S. Pat. Nos. 4,140,216; 3,972,414; 3,859,865; 3,812,732; and 3,713,348. These and other developments in conveyor systems have shown that helical ribbing or grooves along the cylindrical surface of the rollers can be an effective way to improve tracking. Although such ribbing or grooves have improved the tracking ability of these rollers, they have not always increased the realignment rate.
Solutions for improving the realignment rate of tracking rollers have not been significant. One approach to solving the problem has been to use some type of limiter to urge the belt in a certain direction once the belt has moved to a limit position. Although this approach can be helpful in quickly correcting a misaligned belt, it can also cause extensive damage to the edges of the belt or the material travelling over the rollers. In addition, some materials are simply too thin to be realigned in such a fashion. A second approach has been to increase the angle at which the grooves or ribbing are aligned with respect to the circumference of the roller. By increasing the angle at which the helical grooves or ribbing track inward, the speed at which the belt tracks inward can be increased. However, tracking speed can only be increased a limited amount with this approach because once the angle becomes too great the grooves approach being perpendicular to the direction of the belt across the roller, which can result in a loss of all tracking ability.